Thread control mechanism for chainstitch blindstitch machines



T. D. TAYLOR July 30, 1963 7 Sheets-Sheet 1 Filed Nov. 21. 1960 July 30, 1963 T. D. TAYLOR 3,099,236

THREAD CONTROL MECHANISM FOR CHAINSTITCH BLINDSTITCH MACHINES Filed Nov. 21, 1960 7 Sheets-Sheet 2 m l!) CO :0 0 m N Q- 07 I0 1 W (D N 1- l.[ a n m m 8 Q 8 If) N 0) n N .0 Q 03 03 N 8 N o O) 2 IO m N (T: p

FIG. 3

July 3 1963 T. D. TAYLOR 3,099,236

THREAD CONTROL MECHANISM FOR CHAINSTITCH BLINDSTITCH MACHINES Filed Nov. 21, 1960 7 Sheets-Sheet s y 1963 T. D. TAYLOR 3,099,236

THREAD CONTROL MECHANISM FOR CHAINSTITCH BLINDS'I'ITCH MACHINES Filed Nov. 21, 1960 '7 Sheets-Sheet 4 FIG.6

T. D. TAYLOR July 30, 1963 THREAD CONTROL MECHANISM FOR CHAINSTITCH BLINDSTITCH MACHINES Filed NOV. 21, 1960 7 Sheets-Sheet 5 FIG.9

July 30, 1963 T. 0. TAYLOR 3,099,236

THREAD CONTROL MECHANISM FOR CHAINSTITCH BLINDSTITCH MACHINES Filed Nov. 21. 1960 v Sheets-Sheet e T. D. TAYLOR July 30, 1963 THREAD CONTROL MECHANISM FOR CHAINSTITCH BLINDSTITCH MACHINES Filed NOV 21, 1960 '7 Sheets-Sheet 7 bro-m 0.? m 20mm 02502 m EmuZ SE2 2: 3E8 222% 05$; Hafiz .6 5; w

Z ZZZZZZZZQEQQEQQ w wmwmwmmm wmwww o o oooooo ooooo hum 0h FIQE 20mm 02302 m fiumz 3,099,236 TI-READ CONTROL MECHANISM FOR CHAIN- STITCH BLINDSTITCH MAHH-IES Thomas D. Taylor, deceased, late of Hermann, Mo., by Georgia Brueggenjohann, executrix, Hermann, Mo., assignor to Union Special Machine Company, Chicago, 11]., a corporation of Illinois Filed Nov. 21, 1960, Ser. No. 79,861 12 Claims. (Cl. 112-176) This invention relates to mechanism for controlling the tension applied to the single thread employed in a chainstitch blindstitch sewing machine. It involves a thread tensioning device which is automatically operated during each cycle of the machine to apply a desired tension to the thread during a certain portion of the cycle and to release the tension on the thread during another portion of the cycle. The invention also involves a thread nipper mechanism which is operated at will, preferably through a knee press, while the machine is at rest, to apply a tension to the thread at the time the operator is prepared to remove the stitched work from the machine. During the operation of the machine, the nipper mechanism is re- Jcased. Thus, the tension on the thread is controlled entirely by the automatic thread tensioning mechanism while the machine is in operation and it is controlled manual-1y when the work is to be removed. At such time the automatic thread tensioning mechanism will be in portion of the cycle of the machine during which tension is released.

The mechanism contemplated .by the invention is such as to serve effectively a number of different important purposes not heretofore achieved on chainstitch blindstitch machines. It makes possible the production of relatively tight stitches without the puckering and twisting of the work in the course of the seaming operation and without danger of having the stitching thread break strands of the fabric which have been successfully picked up in the course of the blindstitch formation. Puckering and twisting of the work has heretofore occurred when a relatively high tension has been applied to the stitching thread as the looper rolls over the node of fabric and as the feed dog advances the work. The thread, under these conditions has had a tendency to pull the fabric upwardly from the node former. Also, the invention holds to a minimum the breakage of the stitching thread and eliminates the danger of bending the curved needle employed, which could result in breakage of the needle and, in any event, would result in the passage of the needle through too high a point in the node of fabric presented to the needle at the stitch-forming point.

By the provision of a thread nipper which becomes effective in response to the operation of a knee press of the type conventionally employed to enable insertion and removal of the work, the invention facilitates the removal of the work and the severing of the stitching thread without excessive wastage of the latter. The operator simply needs to give the work a quick snap rearwardly after the knee press has lowered the node former and the conventional work supporting means of the machine and has brought the nipper mechanism into active position. The quick snap imparted to the work causes the stitching thread to break over a surface of the looper employed and this leaves about a 2" length of thread extending from the eye of the needle so that the machine is ready for the next seaming operation.

It has been considered necessary heretofore in the construction and operation of chainstitch .blindstitch machines to apply a relatively light tension to the thread at all times as it is fed to the needle, with the result that the stitching formed is relatively loose. This has been 3,099,236 Patented July 30, 1963 Too considered necessary in order to avoid the difiiculties mentioned above resulting from any substantial tension applied to the thread at the time the work is being advanced by a top feed dog and at the time that the looper is being given its conventional rolling and rearward movement while engaged with the loop of thread that has been seized.

In accordance with the invention it has been found possible to apply a reasonably heavy tension to the stitching thread during a predetermined portion of a cycle of operation of the machine, thus enabling the formation of relatively tight stitches without encountering the various difficulties mentioned. The automatic tension mechanism serves to release the tension on the thread during the portion of a cycle of operation of the machine in which the various diflicul-ties would arise if any substantial tension were being applied to the thread. This has been found not to interfere with the production of the desired firm or tight stitches.

With the foregoing purposes and advantages of the invention in view, the invention will now be described in detail as applied to a chainstitch blindstitch sewing machine of the Lewis Model 15 0 Series.

Referring now to the drawings:

FIG. 1 is a vertical sectional view, taken along different planes to show certain of the mechanism within the main horizontally extending arm of the machine and in the base and projecting work arm, of the machine;

FIG. 2 is an elevational view, with several part-s shown in section, of the left end portion of the work arm;

FIG. 3 is a perspective view of the main horizontally extending arm of the machine and the forwardly extending arm which carries the stitch forming and work feeding mechanism, a portion of the frame being broken away to show the interior construction;

FIG. 4 is a front elevational view of a portion of the forwardly extending arm of the machine, With the thread tensioning and nipper mechanism illustrated schematically in relation thereto;

FIG. 5 is a view similar to FIG. 4, showing the stitch forming devices at a different point in their cycle of operation;

FIG. 6 is a horizontal sectional view through the work arm of the machine and the portion of the frame from which it projects;

FIG. 7 is a plan view of the left end of the work arm of the machine, showing the work supporting platens and node former;

FIG. 8 is a view, partly in vertical section and partly in elevation, looking toward the left, showing the main frame of the machine and the work supporting arm;

FIG. 9 is a vertical sectional view through a portion of the base of the machine and the work supporting arm with certain parts shown in a different position from that illustrated in FIG. 8;

FIG. 10 is a vertical section through a portion of the base of the machine and shows, in elevation, the left end of the work arm as mounted thereon;

FIG. 11 is an exploded perspective view of the thread tensioning mechanism which is automatically operated upon each cycle of the machine;

FIG. 12 is an exploded perspective view of the nipper mechanism;

FIG. 13 is a vertical sectional view through one of the elements provided in both the thread tensioning mechanism and the nipper mechanism;

FIG. 14 is a vertical sectional view through the upper portion of the nipper mechanism;

FIG. 15 is a vertical sectional view through the element shown in FIG. 13, taken along a plane at to that along which FIG. 13 has been taken; and

FIG. 16 is a timing chart showing the preferred timing of the operation of the thread tensi-oning mechanism and the feed mechanism, and the time in a cycle of operation when thread is being drawn from the supply, all of these being related to the swinging movement of the needle.

For a more detailed disclosure of certain of the mechanism embodied in the illustrative machine, reference may be had to the following patents:

Mueller, No. 2,109,014, granted February 22, 1938; Mueller, No. 2,416,941, granted March 4, 1947; Mueller, No. 2,588,274, granted March 4, 1952; Mueller et al, No. 2,632,416, granted March 24, 1953; Mueller, No. 2,679,814, granted June 1, 1954.

Referring now particularly to FIGS. 1 and 2, the machine comprises a frame having a base 1t a vertical standard 11, a horizontally extending arm 12 and a work arm 13. The latter is forwardly of and below the arm 12. From the left end of the latter (FIG. 3) there extends, forwardly and slightly downwardly, an arm 14 the forward end of which is disposed above the work arm 13. Within the arm 12 of the frame there is suitably journaled a main drive shaft 15 which extends outwardly from the frame at its right end and is provided with a combined handwheel and pulley 16 through which the shaft may be rotated.

The stitch forming mechanism comprises a curved needle 17 carried by an arm 18 secured to the forward end of a rock shaft 19 journaled within the arm 14. Any suitable connections of the character well known in the art may be provided between the shaft 15 and shaft 19 for rocking the latter upon rotation of shaft 15. Such connections may include an eccentric secured to the shaft 15 within the arm 14 and cooperating with a pitman which is in turn pivotally connected with an arm secured to the shaft 19. Also included in the stitch forming mechanism is a looper 20 which is given a compound movement involving a rolling or oscillatory movement and a longitudinal movement by mechanism of the character disclosed in the Mueller patent, No. 2,588,274. In the course of stitch formation the needle 17 carries a thread through a node formed in the work to be stitched as the point of the needle moves from left to right. While the needle projects from the right side of the node of the work, the pronged end of the looper 20 seizes the loop of needle thread and then, as the needle is retracted toward the left again, the looper by its combined rolling and longitudinal movement carries the seized loop of thread to the left side of the node of the work and mo mentarily retains this loop of thread in the path of the needle -17 so that on the next cycle of the machine the needle passes through this loop. As will be seen from FIG. 3, the prongs of the looper are horizontally spaced as they seize the loop from the needle, and then, as shown in FIG. 5, they are turned into a vertically spaced position by the time the needle enters the seized loop. The looper 20 is then retracted, rolled over the node of the work toward the right side of the latter and then advanced to seize the new loop of needle thread which has been formed at the right side of the node. At an appropriate time in each cycle of stitch formation a feed dog 21 is operated to advance the work toward the rear. The mechanism for operating the feed dog may suitably be of the type disclosed in the Mueller patent, No. 2,109,014. It is given a four-motion movement and serves to press the work against yieldable work supporting platens 23 and 24 (FIGS. 2 and 7) which in turn serve to hold the work upwardly against the undersurface of a fixed presser foot 22. This presser foot is provided with an opening through which the feed dog 21 passes into engagement with the work on the supporting platens. This opening also permits the upward passage of the node former through the presser foot in the manner to be explained. Another opening 25 through the presser foot enables the looper 20 to descend slightly below the upper surface of the presser foot as the looper is rolled over the node of the work, in the manner explained, to position the previ 1 ous loop of needle thread in the path of the needle on its next stitch forming cycle.

For forming a node in the work in the path of the needle, to enable the formation of a blindstitch, there is provided a node former 26 (FIGS. 1 and 2) which is secured to a rock shaft 27. The latter is journaled in a cradle 28 (FIG. 6) pivotally supported by pintles 29 and 30. A relatively strong spring 31 is connected at one end to a pin 31a which extends downwardly from the cradle and is connected at its opposite end to a hook member 32 whose position may be adjusted to vary the tension on the spring. The spring normally retains the cradle in a predetermined position which may be varied in accordance with the depth of penetration of the needle below the top of the node desired for any particular work to be performed. Screw means 33 (FIG. 1) cooperating with the upper surface of the cradle serves to limit the extent to which the cradle is rocked by the spring 31. For details as to this construction reference may be had to the Mueller et al. patent, No. 2,632,416. It will be understood that the spring 31 permits the cradle to rock downwardly about its supporting pintles when an extra thickness of work is encountered by the node former which requires some downward movement of the latter.

For oscillating the node former there is secured to the right end of the rock shaft 27 an arm 34, which carries at ts lower end a ball stud 35 (FIG. 1) surrounded 'by a strap 36 of a link or a short length pitman whose opposite end is pivotally connected with an arm 37 extending upwardly from a member 38. The latter is arranged to turn through a suitable angle upon an eccentric sleeve 39 which is secured to a shaft 40. Another arm 41 which extends downwardly from the member 38 is connected by a screw stud 42 with a pitman 43 which extends rearwardly and upwardly and carries a strap 44 which cooperates with a variable throw eccentric 45 secured to the main drive shaft 15. This variable eccentric is adapted to give one length of stroke to the pitman 43 during one revolution of the shaft 15 and a greater or lesser stroke during the next revolution of the shaft 15, thus providing for a skip stitch operation of the machine. For details as to the construction of the variable eccentric and the means for changing its eccentricity, reference may be had to the Mueller patent, No. 2,679,814.

As also disclosed in said Mueller patent, provision is made for eliminating the skip stitch and providing a 1 to 1 stitch. For this purpose provision is made for shifting slightly the normal position of the eccentric sleeve 39 and shaft 40 in a rotational direction in order to shift slightly the axis about which the member 38 is rocked. By so shifting that axis, the limits of movement of the node former are changed sufficiently so that the node former will present a node of fabric of the same height in the path of the needle upon each operation of the machine, as is required to effect a 1 to 1 stitch. The node former is moved sufficiently to present the full height node in the path of the needle even when the eccentric 45 has its reduced extent of throw. Briefly, the mechanism for this purpose comprises a sector 46 (FIG. 10) secured to a shaft 47. A spring 46:: connected with the sector 46 normally tends to turn the shaft 47 in a clockwise direction (FIG. 10) or counterclockwise direction (FIGS. 8 and 9). Secured to the shaft 47 is a gear 48 which meshes with a gear 49 secured to the shaft 40. Assuming that the parts are normally in the position shown in FIG. 8, it will be seen that if the shaft 40 and its connected eccentric sleeve 39 are turned through a number of degrees, the center of the eccentric, which is the axis about which the member 38 turns, will shift slightly and this will cause a slight change in the two extreme positions of the node former in the course of its movement by the variable eccentric 45'. When it is desired to provide a 1 to 1 stitch an adjustable disc 50 (FIG. 1) secured to the upper end of a shaft 51 may be turned and thus turn a camshaped stop member 52 through a suitable angle. Stop member 52 cooperates with a segment 53 secured to the the mounting of both platens.

shaft 40 and thus limits the extent of rotation of the latter under the force of the spring 46a. For further details as to the operation of the foregoing reference may be had to said Mueller patent, No. 2,679,814.

Referring to FIG. 8, there is shown a knee press 54 connected by an L-shaped rod and socket member with the left end of a rock shaft 55. The latter is urged by a spring 56 in a direction to carry the knee press element toward the right knee of the operator. Spring 56 is connected at its upper end with a pin 57 extending inwardly from a wall of the frame and at its lower end with a pin secured by a collar 58 to the shaft 55. Intermediate its ends, the shaft 55 has secured there-to an arm 59 the form of which is best shown in FIG. 1. This arm is connected by a screw stud 60 with a bar or link 61 (see also FIGS. 8 and 9) and is connected by a screw stud 62 at its upper end to an arm 63 secured to a rock shaft 64. Link 61 has a laterally projecting finger 65 (FIGS. 1 land 8) which is normally spaced a slight distance above a pin or collar 66 carried by the gear 48 at a point removed from the axis of the latter. As the shaft 55 is rotated through a suitable angle by the operation of the knee press 54, the finger 65 will engage the collar 66 and turn the gear 48 through an angle of say, 90. This in turn rotates the gear 49 and thus turns the eccentric sleeve 39 from the position shown in FIG. 8 to that shown in FIG. 9. In so doing the sleeve 39' shifts the member 38 about the axis of the screw stud 42 which is at this time held stationary by the pitman 43. As a result of such movement of member 38 its arm 37 is shifted in a direction to cause the node former to move into a forward position, such as indicated in FIG. 10, in which it readily permits the introduction and removal of work. Also upon release of pressure on the knee press 54 the spring 56 will restore the various parts described into the position indicated in FIG. 8.

Operation of the knee press 54 also serves to lower the work supporting platens 23 and 24. These platens are mounted in a similar manner so that a brief description of the mounting of platen 23 will serve to disclose Pl aten 23 is secured by a bolt to the upper end of an arm 68 pivotally mounted on a member carried by the frame of the machine in axial alinement with the shaft 64. The similar arm for platen 24 is mounted for pivotal movement about an extension of the shaft 64. A spring 69, connected at one end with the machine frame and at the other end with a point on the arm 68 below the axis of shaft 64, serves to swing the arm in a clockwise direction (FIG. until an extension 70 of the arm 68 engages a bar or bracket 71 secured to and rotatable with the shafit 64. As shaft 64 is rotated or rocked by the operation of the knee press, in the manner explained, it will cause the bar or bracket 71 to turn in a counterclockwise direction (FIG. 10) thus turning the arm 68 for each platen in the same direction and lowering both of the platens 23 and 24. This, it will be understood, takes place at the same time that the node former is shifted into an inactive position to permit the insertion or removal of work.

Referring now to FIGS. 3, 4 and 5, stitching thread 72 is led from a suitable supply to a nipper mechanism 73, then to an automatic tension device 74, then to an eyelet 75 at the rear end of the arm .14, then to an eyelet '7-6 at the forward end of the latter arm and downwardly to an eyelet 77 of the needle arm 18 from which it is passed through the eye of the needle 17 with a suitable amount of thread extending beyond the needle eye. If desired, the guide element 75 may be omitted and the thread may be passed directly from the tensioning mechanism 74 to the eyelet 76, as shown in FIGS. 4 and 5. However, the arrangement shown in FIG. 3 is preferred.

The nipper mechanism 73 is best shown in FIGS. 3, 12, 13, 14 and 15. It comprises a post having an upper screw threaded stem portion 78, an intermediate collar 79 and a lower screw threaded portion 80. The portion 78 is provided with a longitudinally extending slot 78a for the greater portion of its length, this slot extending completely across the diameter of the portion 78. A lock nut '81 has threaded engagement with the pontion 80 and beneath this lock nut is mounted a plate 82 having an upwardly extending pin 83. The lower end of threaded portion 80 of the post described has threaded engagement with a sleeve 84 extending downwardly from a cover plate 85 at the top of the vertical standard of the machine frame. The arrangement is such that the height of the post in relation to the plate 85 may be varied slightly and it may be locked in said position by the nut 81.

Two saucer-like discs 86 and 87 are mounted in inverse relation on the stem 78. The thread 72 is passed between these two discs to impant a nipping action to the thread at the appropriate time. The discs are prevented from rotation by the cooperation of notches 86a and 87a with the pin '83. A cupped member 88 is mounted above the disc '87 and arranged to transmit the force of a spring '89 to the two discs at the appropriate time. Member 88 has two semi-circular openings 88a and 88b at opposite sides of a cross bar 88c. The latter is arranged to slide within the slot 78a of the threaded stem 78 while the two sections of the latter pass through the openings 38a and 88b. Spring 89 is held upon the stem 78 by a nut 90 which may be turned to provide the desired amount of compression force in the spring 89.

With the parts as shown in FIG. 14 the thread passing between the discs 86 and 87 will be subjected to a substantial frictional force which provides the desired nipping action. However, as has been stated, the machine is so constructed that normally the force of the spring 89 will be counteracted so that little, if any, frictional resistance will be imparted to the thread. For this purpose a rod 91 extends upwardly through the post and is normally held in a sufiiciently elevated position to engage the cross bar 880 of the cup member 88 and force the latter upwardly out of engagement with the disc 87, thus counteracting the force of the spring 89. At its [lower end the rod 91 passes through a fixed bar or bracket 92 into engagement with the upper end of an arm 93 secured to the rock shaft 55. The latter, as has been explained, is normally urged in a clockwise direction (FIG. 3) by a spring 56 which is of substantially greater force than the spring 89. The extent to which the shaft 55 is thus turned by spring 56 is limited by the engagement of a collar 94, secured to the rod 91, with the undersurface of the bar 92. This is sufiicient to cause the upper end of rod 91 to lift the cup member '88 away from disc 87. However, when the shaft 55 is turned by the operation of the knee press 54, the arm 93 will be turned in a counterclockwise direction (FIG. 3) and the spring 89 will be permitted to force the cup member 88 against disc 87 and the latter against disc 86 to produce the nipper action mentioned.

The details of the automatic tension mechanism 7-4 are best shown in FIGS. 1, 3 and 11. It comprises a sleeve 95 threaded into the top of the arm 12 of the frame of the machine. Sleeve 95 has a nut-like portion 95a at its upper end, a screw threaded portion 95b and a cylindrical portion 95c at its lower end which is of slightly reduced diameter. 'A post 96 having the same construction as the post 78, above described, has screw threaded engagement with an opening 95d in the sleeve 95. A lock nut 97 threaded onto the lower threaded portion of post 96 enables the latter to be locked in adjusted position in relation to the sleeve 95. Thus, the height of the post 96 above the top of sleeve 95 may be varied slightly to vary the duration of the release of tension on the thread during a cycle of the machine. Discs 98 and 99, provided respectively with notches 98a and 99a, are applied over the upper threaded end of the post 96 and rest upon the collar portion of the post. A pin 9% carried by the frame of the machine cooperates with the notches 98a and 99a to prevent rotation of the discs. Above the disc 99 is a cup member 100 which coacts with the lower end of a spring 101. At the upper end of the post 96 there is provided a nut 102 which may be turned to vary the spring force exerted upon the discs 98 and 99 during the portion of a cycle of the machine in which tension is applied to the thread. Extending upwardly through bores within the sleeve 95 and post 96 is a rod 103 the upper end of which is adapted to cooperate with a cross bar 10% of the cup member 100. The lower end of rod 103 engages an eccentric portion 104 of a sleeve 105 secured to the main drive shaft '15 by one or more screws .106. The arrangement is such that when the rod 10? engages the high portion of the eccentric 104 extending over an arc of from 90 to 150, the upper end of the post will hold the cup member 100 raised sufficiently to prevent transmission of any force from the spring 101 to the discs 98 and 99. When the lower end of rod 103 engages the remaining low portion of the eccentric, the upper end of the post will become disengaged from the cross bar 10051 of the cup member 100 and thus permit the spring 101 to apply its thread tension producing force. By turning the sleeve 105 in relation to the shaft and then setting it by tightening the screw or screws 106, it is possible to vary the time in a cycle of the machine during which the tension is released and during which it is applied.

Referring now to FIG. 16 there is shown diagrammatically a preferred timing of certain operations performed during a single cycle of operation, its. one revolution of the main drive shaft, for Lewis machines of any of the 150 styles with the exception of Model 150-9. A cycle is considered as beginning when the needle is in its leftmost position and is about to move toward the right. The lower half of the diagram is identified with the movement of the needle toward the right during the first 180 of the revolution of the main drive shaft while the upper half of the diagram is identified with the movement of the needle from right to left during the 1803 60 move ment of the main drive shaft. The needle is given a stroke of 51%" in each direction. During the first 90 of the cycle the point of the needle passes through and slightly to the (right of the node of the fabric being stitched while during the next 90 of the cycle the point of the needle continues to move toward its extreme righthand position. This means that the node of fabric is positioned somewhat to the left of the center point of the line of travel of the point of the needle. During the first 40 of a cycle the feed dog is advancing the material and at the 40 point the tension discs of the automatic tension mechanism are closed and they remain closed throughout the balance of the 180 portion of the cycle and still remain closed up to the 250 point of the cycle. From about 90 to 160 of the cycle thread is being drawn from the supply, due to the drawing action of the needle in its-movement toward the right. The amount of thread so drawn is only A" in length. A greater amount of thread is drawn during the last half of the cycle beginning at about the 240 point and extending to the 350 point. During this time 1" of needle thread is drawn and this is due largely to the action of the looper as it rolls over the top of the node from right to lefit and is due in part to the advancing of the material by the top feed dog. Such advance of the material begins at about the 290 point in the cycle, continues through to the 360 point and carries on for the first 40 in the next cycle of the machine. It will be understood that the amount of thread drawn from the source of supply during each cycle of the machine varies somewhat with the number of stitches per inch. The total of 1 A of thread drawn during a cycle, in the example given, is on the basis of four stitches per inch.

The preferred timing explained above is such that release of tension on the needle thread begins at the 250 point in a cycle when the needle eye is within of the right edge of the opening through which the'node of fabric is projected upwardly, during the movement of the needle from right to lefit. Tension is not reapplied to the needle thread until the point of the needle, on its movement from left to right, enters between the prongs of the looper, which occurs at about the 40 point of a cycle. It will be understood that at this time the loop, which was previously seized by the looper on the right side of the node and carried over the top of the latter and then downwardly and rearwardly into position to pennit passage of the needle therethrough, is withdrawn by the needle from the looper as the latter continues its rearward movement.

In order to achieve the foregoing timing of the various operations the cam 104 must be appropriately set in the required angular position with respect to the shaft 15. Also to achieve the desired duration of thread tension release the post 96 must be adjusted vertically in relation to the supporting sleeve '95. It has been found that this will normally occur when the post, after being bottomed in relation to the sleeve 95, is turned outwardly approximately 1 /2 turns. The lock nut 97 may then be tightened to retain the post in such set position.

For the Model -9 Lewis machines it has been found desirable to adjust the thread tension assembly so that it releases tension on the thread when the point of the needle, on its return movement from right to left, is about even with the left side of the cloth opening in the presser foot through which the node of fabric is projected upwardly. This occurs when the point of the needle is at about the 270 point in the cycle. Tension is preferably reapplied when the needle is at the extreme leftmost position of its stroke. To achieve this timing it has been found that the tension post 96 must be turned outwardly approximately 1% turns from its bottomed position in relation to the sleeve 95.

While some latitude is permissible in the precise timing of the application and release of tension to the thread by the automatic tensioning mechanism, it has been found desirable to stay reasonably closely within the limits discussed above, in order to produce a relatively tight stitch without running into the various difiiculties mentioned at the beginning of this specification. It is of primary importance in the operation of the chainstitch blindstitch machine that a relatively heavy tension be applied to the stitching thread during the major portion of a cycle of the machine but that it be released during the period in which the needle is moving :away from the work while the looper with its seized loop is rolling over the node of fabric. in most instances it is important to have the thread tension released throughout the :feeding of the work and during the period that the looper is pulling the seized loop of thread rearlwardly. Also it is important that the thread be subjected to a nipper action as the work is being removed from the machine, since the needle at such times must be retracted from the work and preferably in about its leftmost position. The automatic tension will at such times be released.

What is claimed is:

'-1. In a single thread chainstitch blindstitch sewing machine having -a curved thread-carrying needle, means for carrying said needle for movement along an arcuate path at right angles to the line of stitch formation, a reciprocatory and oscillatory looper, a node former for forming a node in the fabric to the stitched in the region of stitch formation, the oscillation of the looper serving to carry a loop of thread seized from the needle on one side of said node to the opposite side thereof, a .top feed dog, and a main drive shaft with connections therefrom for operating said needle, looper, node former and feed dog, the combination which comprises a thread tensioning device including members mounted for movement toward each other between which the thread is passed, a single spring for urging said members together to apply a selected tension to said thread, adjustable means in said device for varying the selected tension normally applied 9 to the thread as it is fed to the needle, and connections from said main drive shaft for completely releasing the tension norm-ally applied by said adjustable means during a portion of each revolution of said drive shaft.

2. A sewing machine for the character set forth in claim 1 in which said connections from said main drive shaft for releasing the tension on said thread comprises a cam secured to said drive shaft and connections therefrom for eifecting release of said tension by the time the point of the needle is Withdrawn from the noded fabric and continuing such release as the point of the needle is moved to its maximum distance away from the fabric.

3. A sewing machine of the character set forth in claim 2 in which said cam has a surface of such con,- figuration cooperating with said connections. therefrom as to continue the release of tension on said thread until the point of the needle is about to enter the noded fabric for the formation of the next stitch.

4. A sewing machine of the character set forth in claim 2 in which said cam has a surface of such configuration cooperating with said connections therefrom as to release the tension on said thread as the looper in the course of the oscillating movement begins to carry the seized loop of thread over the noded fabric toward the opposite side thereof and as to continue such release of tension until the point of the needle on its next cycle enters the seized loop of thread so carried over by the looper.

5. A sewing machine of the character set forth in claim 1 in which means are provided for mounting and driving said looper to impart thereto longitudinal co ponents of movement in opposite directions substantially parallel with the line of feed and rolling components of movement in opposite directions transverse to the line of feed, said connections from said drive shaft for releasing tension on said thread comprising a cam on said shaft and connections therefrom to said tension applying means serving to release the tension on said thread as the needle moves trom its furthermost position away from the work to a position in which it is about to enter the noded work and as the needle on its return movement is about to leave the noded work until it reaches its furthermost position away from the work.

6. A sewing machine of the character set forth in claim 5 in which said cam and the connections therefrom are so formed and positioned as to release tension on said thread for substantially 150 of each revolution of said drive shaft.

7. A sewing machine of the character set forth in claim 2 in which said cam and the connections therefrom are so formed and positioned as to release tension on said thread during substantially from to of each revolution of said drive shaft.

8. A sewing machine of the character set forth in claim 1 having a normally inoperative nipper mechanism for applying tension to the thread, and means operable at will by the operator for causing said nipper mechanism to apply tension to said thread.

9. A sewing machine of the character set [forth in claim 2 having a normally inoperative nipper mechanism for applyin g tension to the thread, and means operable at will by the operator for causing said nipper mechanism to apply tension to said thread.

10. A sewing machine of the character set forth in claim 9 in which said means operable at will is operable on said nipper mechanism when the main drive shaft is in a position in which said adjustable means for applying tension to the thread is released, thereby applying tension to said thread as the work is removed from the machine.

11. A sewing machine of the character set forth in claim 10 having means connecting said means operable at will with said node former to shift the latter out of engagement with the work as said nipper mechanism is operated to apply tension to said thread.

'12. A sewing machine of the character set forth in claim 10 having a stationary presser foot, work supporting means beneath said presser foot, spring means connected with said work supporting means for normally urging work upwardly against said presser foot, and connections :from said means operable at will for moving said work supporting means downwardly against the action of said spring means.

References Cited in the file of this patent UNITED STATES PATENTS 1,588,134 Mueller June 8, 1926 2,128,033 Zonis Aug. 23, 1938 2,601,054 Parry June '17, 1952 2,685,267 Maxant Aug. 3, 1954 2,763,225 Mensching Sept. 18, 1956 FOREIGN PATENTS 513,904 Germany Dec. 4, 1930 

1. IN A SINGLE THREAD CHAINSTITCH BLINDSTITCH SEWING MACHINE HAVING A CURVED THREAD-CARRYING NEEDLE, MEANS FOR CARRYING SAID NEEDLE FOR MOVEMENT ALONG AN ARCUATE PATH AT RIGHT ANGLES TO THE LINE OF STITCH FORMATION, A RECIPROCATORY AND OSCILLATORY LOOPER, A NODE FORMER FOR FORMING A NODE IN THE FABRIC TO BE STITCHED IN THE REGION OF STITCH FORMATION, THE OSCILLATION OF THE LOOPER SERVING TO CARRY A LOOP OF THREAD SEIZED FROM THE NEEDLE ON ONE SIDE OF SAID NODE TO THE OPPOSITE SIDE THEREOF, A TOP FEED DOG, AND A MAIN DRIVE SHAFT WITH CONNECTIONS THEREFROM FOR OPERATING SAID NEEDLE, LOOPER, NODE FORMER AND FEED DOG, THE COMBINATION WHICH COMPRISES A THREAD TENSIONING DEVICE INCLUDING MEMBERS MOUNTED FOR MOVEMENT TOWARD EACH OTHER BETWEEN WHICH THE THREAD IS PASSED, A SINGLE SPRING FOR URGING SAID MEMBERS TOGETHER TO APPLY A SELECTED TENSION TO SAID THREAD, ADJUSTABLE MEANS IN SAID DEVICE FOR VARYING THE SELECTED TENSION NORMALLY APPLIED TO THE THREAD AS IT IS FED TO THE NEEDLE, AND CONNECTIONS FROM SAID MAIN DRIVE SHAFT FOR COMPLETELY RELEASING THE TENSION NORMALLY APPLIED BY SAID ADJUSTABLE MEANS DURING A PORTION OF EACH REVOLUTION OF SAID SHAFT. 